arXiv subjects

Andrey Katz

Publications and source records attributed to Andrey Katz.

51 records · Page 3Linked to original sources

arXiv2010

Jet Substructure and the Search for Neutral Spin-One Resonances in Electroweak Boson Channels

Strongly coupled models at the TeV scale often predict one or more neutral spin-one resonances (Z') which have appreciable branching fractions to electroweak bosons, namely the Higgs and longitudinal W and Z. These resonances are usually believed to have multi-TeV mass due to electroweak precision constraints, placing them on the edge of LHC discovery reach. Searching for them is made particularly challenging because hadronically decaying electroweak bosons produced at such high energy will appear very similar to QCD jets. In this work we revisit the possibility of discovering these resonances at the LHC, taking advantage of recently developed jet substructure techniques. We make a systematic investigation of substructure performance for the identification of highly Lorentz-boosted electroweak bosons, which should also be applicable to more general new physics searches. We then estimate the model-independent Z' discovery reach for the most promising final-state channels, and find significant improvements compared to previous analyses. For modes involving the Higgs, we focus on a light Higgs decaying to b quarks. We further highlight several other novelties of these searches. In the case that vertex-based b-tagging becomes inefficient at high p_T, we explore the utility of a muon-based b-tag, or no b-tag at all. We also introduce the mode Z' -> Zh -> (invisible)(bb) as a competitive discovery channel.

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arXiv2010

Direct Gaugino Mediation

We describe renormalizable supersymmetric four-dimensional theories which lead to gaugino mediation and various generalizations thereof. Even though these models are strongly coupled, we can demonstrate the parametric suppression of soft scalar masses via Seiberg duality. For instance, we show that our models have a parameter which continuously interpolates between suppressed soft scalar masses and their conventional gauge mediated contribution. The main physical effect which we utilize is the general relation between massive deformations in one frame and higgsing in the dual frame. Some compelling and relatively unexplored particle physics scenarios arise naturally in this framework. We offer preliminary comments on various aspects of the phenomenology and outline several of the outstanding open problems.

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arXiv2010

Leptophilic Signals of a Sneutrino (N)LSP and Flavor Biases from Flavor-Blind SUSY

Although the sneutrino is a viable NLSP candidate with gravitino LSP, spectra of this type occupy a part of SUSY parameter space in which collider signatures are poorly studied. In this paper we will extend previous work on this topic to include sneutrino NLSP spectra with non-minimal phenomenology. Generally, these spectra exhibit very leptophilic behavior, which can be easily observed at the LHC. We show that a variety of such spectra can be analysed with similar techniques, leading in each case to very suggestive evidence for complicated decay chains that end in sneutrinos. Amongst the variations considered, we find a simple class of spectra that produce signals with strong electron-muon asymmetries. These signals could naively be interpreted as evidence for lepton flavor violation, but can occur even with flavor-blind SUSY.

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arXiv2010

Signals of a Sneutrino (N)LSP at the LHC

The sneutrino is a viable candidate for the NLSP in SUSY spectra with gravitino LSP. In this work we study the collider implications of this possibility. In particular, we investigate whether the LHC can distinguish it (at least, in some cases) from alternative spectra, such as those with a neutralino LSP. We show that there exists a complete family of experimentally allowed and theoretically motivated spectra with sneutrino NLSP, which exhibit very distinctive multilepton signals that are difficult to fake within the MSSM. We study these signals in detail, including the techniques necessary to find them. We demonstrate our analysis approach on simulations incorporating backgrounds.

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arXiv2009

On the Thermal History of Calculable Gauge Mediation

Many messenger models with realistic gaugino masses are based on meta-stable vacua. In this work we study the thermal history of some of these models. Analyzing R-symmetric models, we point out that while some of the known messenger models clearly prefer the supersymmetric vacuum, there is a vast class of models where the answer depends on the initial conditions. Along with the vacuum at the origin, the high temperature thermal potential also possesses a local minimum far away from the origin. This vacuum has no analog at zero temperature. The first order phase transition from this vacuum into the supersymmetric vacuum is parametrically suppressed, and the theory, starting from that vacuum, is likely to evolve to the desired gauge-mediation vacuum. We also comment on the thermal evolution of models without R-symmetry.

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arXiv2009

Uplifted Metastable Vacua and Gauge Mediation in SQCD

Anomalously small gaugino masses are a common feature of various models of direct gauge mediation. This problem is closely related to the vacuum structure of the theory. In this paper we show that massive SQCD can have SUSY-breaking vacua which are qualitatively different from the ISS vacuum. These novel vacua are metastable with respect to decay to the ISS vacuum. We demonstrate the possibility of addressing the gaugino mass problem in this framework. We study the properties of these vacua and construct an example of a model of direct gauge mediation.

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arXiv2009

Breaking the Dark Force

Recently Arkani-Hamed, Finkbeiner, Slatyer and Weiner proposed a unified explanation to the set of experimental and observational anomalies with possible connections to Dark Matter (DM). A central role is played by GeV scale "dark" gauge bosons exchanged by the weak scale DM. Motivated by this proposal, we build an explicit model of DM in the context of Weak Scale Supersymmetry (SUSY). We employ high-scale SUSY-breaking and invoke the Giudice-Masiero mechanism to generate the weak scale DM masses. By sequestering the dark sector from the SUSY-breaking "hidden" sector, it naturally acquires GeV scale soft masses that help generate the dark gauge boson mass. The visible MSSM sector is not fully sequestered and acquires gaugino-mediated soft terms at the weak scale. This hierarchy of scales naturally leads to the Sommerfeld enhancement of DM annihilations needed to account for the electron/positron excesses in the PAMELA and ATIC experiments. The possibility of co-existing species of DM is used to show how the INTEGRAL and DAMA anomalies can both be explained. We study the cosmological constraints on the new stable or long-lived light particles that appear in our models. We discuss the lepton-jet collider signals suggested by Arkani-Hamed and Weiner, and find that they are not guaranteed in our construction.

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arXiv2008

Dynamical SUSY and R-symmetry breaking in SQCD with massive and massless flavors

We show that supersymmetry and R-symmetry can be dynamically broken in a long-lived metastable vacuum of SQCD with massive and massless flavors. The vacuum results from a competition of a (leading) two-loop effect and small "Planck" suppressed higher-dimension operators. This mechanism provides a particularly simple realization of dynamical SUSY and R-symmetry breaking, and as such it is a good starting point for building phenomenologically viable models of gauge mediation. We take a preliminary step in this direction by constructing a complete model of minimal gauge mediation. Here we find that the parameters of the model are surprisingly constrained by the hidden sector. Similar mechanisms for creating long-lived states operate in a large class of models.

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arXiv2008

On SQCD with massive and massless flavors

We consider supersymmetric QCD in the free magnetic phase with massless and massive flavors. The theory has a supersymmetry breaking pseudo-moduli space of vacua and a runaway behavior far away from the origin. A two-loop computation reveals that the origin is destabilized and there is no meta-stable SUSY breaking solution. We also study the embedding of this model in type IIA string theory and find evidence for similar behavior. The perturbative brane dynamics involves simple interactions between branes, correctly predicting the two-loop result in the gauge theory. Our results also apply to the case when all the flavors are massive but have hierarchy among them, leading to possible instability which is manifest both in field theory and the brane description.

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arXiv2007

Local SUSY-breaking minima in N_f=N_c SQCD?

We study non-supersymmetric minima in N_f=N_c SQCD conjectured by Intriligator, Seiberg and Shih (ISS). We show that the existence of such minima depends on the signs of three non-calculable parameters and that no evidence can be inferred by deforming the theory. We illustrate this by demonstrating that the conjectured minimum is destabilized in a different deformation of N_f=N_c SQCD. We also comment briefly on the phenomenological consequences of this instability.

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arXiv2007

Comments on the Meta-Stable Vacuum in N_f=N_c SQCD and Direct Mediation

We revisit N_f=N_c SQCD and its non-supersymmetric minima conjectured by Intriligator, Seiberg and Shih (ISS). We argue that the existence of such minima depends on the signs of three non-calculable parameters and that no evidence can be inferred by deforming the theory. We demonstrate this by studying a deformation of the theory which involves additional gauge singlets. In this case, the conjectured minimum is destabilized. We comment on the consequences of such singlets in models of direct mediation and in particular in the Pentagon model.

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arXiv2007

Lorentz Violation and Superpartner Masses

We consider Lorentz violation in supersymmetric extensions of the standard model. We perform a spurion analysis to show that, in the simplest natural constructions, the resulting supersymmetry-breaking masses are tiny. In the process, we argue that one of the strongest bounds on Lorentz violation in the photon Lagrangian, which comes from the absence of birefringence from distant astrophysical sources, does not apply when Lorentz violation is parametrized by a single vector.

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arXiv2006

Supersymmetry breaking and the radion in AdS_4 brane-worlds

We compute the one-loop correction to the radion potential in the Randall-Sundrum model with detuned brane tensions, with supersymmetry broken by boundary conditions. We concentrate on the small-warping limit, where the one-loop correction is significant. With pure supergravity, the correction is negative, but with bulk hypermultiplets, the correction can be positive, so that the 4d curvature can be lowered, with the radion stable. We use both the KK theory, and the 4d radion effective theory for this study.

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arXiv2006

Supersymmetry Breaking and Moduli Stabilization in AdS

We study the one loop effective potential for the radion superfield in the supersymmetric Randall-Sundrum scenario with detuned brane tensions. At the classical level the distance between the branes is stabilized while the VEV of the fifth component of the graviphoton is a flat direction which breaks supersymmetry. At the quantum level a potential is generated. This leads to a toy model of a supersymmetric compactification with all the moduli stabilized perturbatively.

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arXiv2004

Gauge Theories in $AdS_5$ and Fine-Lattice Deconstruction

The logarithmic energy dependence of gauge couplings in AdS_5 emerges almost automatically when the theory is deconstructed on a coarse lattice. Here we study the theory away from the coarse-lattice limit. While we cannot analytically calculate individual KK masses for a fine lattice, we can calculate the product of all non-zero masses. This allows us to write down the gauge coupling at low energies for any lattice-spacing and curvature. As expected, the leading log behaviour is corrected by power-law contributions, suppressed by the curvature. We then turn to intermediate energies, and discuss the gauge coupling and the gauge boson profile in perturbation theory around the coarse-lattice limit.

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